1. Field of the Invention
The present invention relates to a linear motion guide unit that is composed of a sliding element movable through rolling elements along a track rail in a sliding manner.
2. Description of the Prior Art
Conventionally a linear motion guide unit shown in FIGS. 11 to 13 is well known to those skilled in the art.
The prior linear motion guide unit, as shown in FIGS. 11 to 13, comprises a track rail 1 fixed to a mounting base 30 and having opposing lengthwise side surfaces 24 on which are formed raceway grooves 22, a sliding element, or slider 2, saddling on a track rail 1 so as to freely move along and with respect to the track rail. The slider 2 is composed of a casing 3 formed with raceway grooves 23 confronting the raceway grooves 22 of the track rail, rolling elements 7 running through raceways defined between the confronting raceway grooves 22, 23 so as to permit the slider to move relatively to the track rail, end caps 4 arranged on the end surfaces 19 opposed in the moving direction of the slider or lengthwise, one to each end surface, end seals 5 secured at 20 on the end caps 4 so as to close clearances between the track rail 1 and the slider 2, and bottom seals 26 arranged on the lower surfaces o f th e casing and the end caps 4. The casing 3 is further formed with threaded openings for attaching thereto other appliances, parts or the like by screws.
The bottom seals 26 are to cover the lower surfaces of the casing 3 and end caps 2 and further close clearances between the casing 3 and the end caps 4. The slider 2 saddles on the track rail 1 so as to smoothly move in a sliding manner by virtue of rolling elements of balls, or rollers, circulating along the raceway grooves 22 on the track rail 1. The rolling elements 7 may run in a circulating manner through raceways 29 defined between the confronting raceway grooves 22, 23, turnaround paths, not shown, formed in the end caps s and return paths 25 in the casing 3. Grease nipples 27 are provided at end surfaces 28 of the end seals 5 for supplying lubricant to the raceways 29 and the rolling elements 27.
The bottom seals 26 for the slider 2 are each provided at a lengthwise edge thereof with a lip, not shown, which extends along the lower surfaces of the casing 3 and end caps 4 so as to make tight contact with the opposing lengthwise side surfaces 24 of the track rail 1. The bottom seals 26 are secured to the casing 3 and end caps 4 with screw fastenings not shown in the accompanying drawings. As described just above, because the bottom seals have been conventionally attached to the casing 3 with the fastenings such as rivets, screws or the like, attachment and/or detachment of the bottom seals has been troublesome. Moreover, the bottom seals 26, although simple in shape and easy in production, have many disadvantages in which positional error is liable to happen in matching with the casing 3 and the track rail 1, and further the bottom seals are so thin as to be easy to deform due to external forces, thermal stress or the like. Hence, the conventional bottom seals 26 have a major problem in which they undergo deformation such as lengthwise distortion that is caused by swelling owing to lubricating oil, elongation and/or shrinkage owing to temperature change at the seals 26 resulting from the sliding motion of the slider 2 on the track rail 1, whereby the sealing performance deteriorates.
Disclosed in Japanese Utility Model Laid-Open No. 51549/1994 is dust-proof sealing means for linear motion guide units. In the linear motion guide unit in the above citation, the dust-proof bottom seals are fitted at their lengthwise major sections in the slots formed at the lower sides of the end caps. The bottom seals are further held at their opposing upright ends in the recesses formed on the end surfaces of the end caps. The recesses formed on the end caps each have a contour extending laterally outwardly at its inner part while the upright ends also extend at their distal ends externally outwardly so as to fit into the recesses.
Another types of the bottom seals have been further disclosed in, for example, Japanese Patent Laid-Open No. 71455/1995 and Japanese Utility Model Laid-Open No. 49824/1994. The prior bottom seals consist of core plates and elastic members adhering to the core plates and mounted to the lower sides of the casing and end caps with making use of spaces that are left for attaching the whetstones to grind the track rail. For mounting or incorporating the bottom seals to the end caps of the slider, the bottom seals have the upright brackets formed integrally with the core plate and, on the other hand, the end caps are provided with slots to be engaged with the brackets of the bottom seals. As an alternative, the bottom seals have hooks that are formed at the distal ends of the brackets towards lengthwise inwardly of the seals so as to make engagement with slits or holes in the end caps.
Meanwhile in the prior linear motion guide units, the bottom seals have been optionally mounted to the lower surfaces of the casing and end caps in accordance with the models of the units. The mounting of the bottom seals, however, has been recently recognized as a major problem. The cause of the problem resides in a rapidly increasing requirement for miniaturization of the linear motion guide units and therefore a tendency of the acceptable length of the end caps becoming shorter and shorter. This recent trend towards the shorter end cap in the slider is making it much more difficult to form the slots or holes in the end cap for engagement with, for example, the hooks that are provided by bending lengthwise inwardly the distal ends of the brackets of the bottom seals, as disclosed in the above-cited linear motion guide units.
In the dust-proof sealing means for linear motion guide units disclosed in the above-cited Japanese Utility Model Laid-Open No. 51549/1994, the end caps are each provided at its lower surface with slots and also at its end surface with the recess. The dust-proof bottom seals each have the opposing upright ends of a contour extending at their distal ends externally outwardly. On attaching the bottom seals to the end caps, the bottom seals are fitted in the slots at their lengthwise major sections. The bottom seals are in addition held at their opposing upright ends in the recesses. This cited mounting system of the bottom seals also disadvantageously requires the provision of slots and recesses in the end caps in order to help ensure the reliable mounting of the bottom seals.